I find the addition of a center microphone position to be one of the most useful things when running multi-mic stereo configurations (configs meant for mixing together, rather than those intended for comparison or back-up purposes). It provides control over dialing in the most appropriate balance between a solid phantom center and a nice wide stereo feel, allowing optimization of both qualities in a recording without compromise. Just be prepared to space the mics sufficiently so that the center mic has room to do it's job, at least twice the total spacing you would use for a two microphone configuration. You want the L/R pair arranged in such a way that if the center mic was not present you'd get a hole in the middle of the playback image. If the L/R mic pair configuration would work fine without the center mic, then it's not an optimal configuration for 3-microphone stereo.
I use either a supercard or cardioid in the center, but a single shotgun should substitute, possibly working better in some situations if not behaving as well in others. I've not used either the ck63 nor the NTG3 myself, but write this assuming the ck63 has superior performance in terms of the quality of it's off-axis pickup and how it sounds when used as a straight stereo pair in a good acoustic. If that's indeed the case, then I'd either:
Let one of the NTG3s go and pickup the pair of ck63s..
consider letting both NTG3s go to pickup three ck63s
Below is what has worked for me and seems applicable here. My intention in outlining this is more to illustrate how one can build on and extend the basic 3-microphone configuration as a starting point rather than offering specific suggestions for doing so, because I think the basic concept is what is most important and should work well for anyone even though the specifics of how it's implemented will vary-
In a boomy mid-sized room, I've had good results running three supercards in a spaced configuration with the center mic pointed directly forward and the left/right mics pointed +/- 45 degrees (not overly far from PAS, mics ending up pointing maybe +10 degrees or so outside of the hanging PA arrays), spaced as far apart as I could manage on the bar I use for doing that, which is around 2' apart or so total. You could try something similar substituting the single shotgun for the center supercardioid and I'd expect it to work in much the same way. In your case the spaced/angled L/R supercard pair should help smooth the off-axis irregularities which the center shotgun might exhibit.
In better sounding rooms, switch the L/R supercards to cardioids, angled the same +/- 45 degrees and spaced a bit further apart, or spaced the same and angled further apart.
Outdoors, switch the L/R pair to omnis and space them even further if you can, like up to 5' or so. But if you can't don't sweat it, the same 2' total spacing will still work when using omnis.
..and in any of those situations, turning that single center microphone, regardless of pickup pattern, into a coincident stereo arrangement becomes a very useful advantage and takes things to the next level. Consider picking up a single inexpensive figure-8 to play around with doing that. I use a Naiant X-8S, which cost just $150, and place it directly beneath my center mic. It's acts as a totally optional Side channel, and allows me to blend the solid central image provided by the single forward-facing microphone outwards into the wide left/right stereo field "bed" by dialing as much mid/side width as necessary to get a seamless image across the entire stereo field. I don't have to use that channel at all, in which case the microphone config is straight 3-mic stereo, but I almost always end up using some of it. That allows me to use more center mic in the stereo mix, enhancing center solidity and clarity, without the center sticking out and sounding isolated and "unglued" from the left/right image. It takes what the addition of the center mic contributes and makes that even more useful by providing a center blend control. The resulting microphone configuration might be best described as still being 3-point stereo, consisting of a single-point M/S pair placed between a spaced L/R pair, only using 4 microphones instead of three in a way which retains the superior qualities of the simple 3 mic arrangement.
Without a bi-directional (fig-8) to turn that center mic into a M/S pair, you can still do something similar with the mics you'll already have on hand, but it will require recording an extra channel.
To do so, use either the cardioids or supercards-
When using the supercards as your wide PAS L/R pair, arrange the cardioids in X/Y directly under or over the forward facing center microphone, but angle that X/Y pair 180 degrees apart, each mic facing directly to the side. Don't worry about trying to do any M/S stuff, instead just route the pair to Left/Right as you would any typical stereo pair and add just as much as you need to widen the strong, solid center you get from main forward pointed center mic until it blends perfectly with the L/R ambient bed.
When using the omnis as your wide L/R pair, arrange the supercardioids in X/Y exactly the same way. You can also play with arranging this sideways pointing (center stereoizing) mic pair so that the mics are are spaced rather than coincident, which works well when using very widely-spaced omnis as your L/R mics outdoors. In that case, you can space the sideways facing pair up to ~2' apart or so if the omnis are at least 4' apart or more.
All those options build upon a simple 3-microphone starting configuration. All but the last suggestion retains the use of just 3 mic positions in space - Left, Center, and Right - even though some of them may use 4 or 5 microphones. The last suggestion uses 5 microphone positions, but only once the omnis are spaced far enough away that there is room in the center to branch out without turning things into a mess.